Injection molded plastic containers and lock-on closures are in popular use for packaging a wide variety of products in quantities of one to six gallons. Examples include asphalt sealant, paint, drywall putty and food products. The “lock-on” feature is typically provided by an undercut in the closure which snaps around a peripheral edge flange in the open top of the container. The hoop strength of the closure is such that means must be designed into the closure to facilitate its removal. The two most common such means include (1) tear strips which are removed to reduce the force of the locking mechanism and (2) windows or apertures in the closure skirt which permit the skirt to be fractured at several circumferentially spaced locations. These mechanisms can also be used in combination.
Prior art tear strips can be difficult for a user to access and to grip as the tab is broken away and the tear strip is removed from the outer periphery of the closure. To solve this problem, some prior art closures have been designed to provide a tab that protrudes outwardly from the skirt of the closure for easier access. However, this method prevents efficient stacking of closures for storage.
Efforts to design strength into the closure generally involve adding thickness to the closure skirt. This approach uses additional plastic material, adds weight and can give rise to warpage problems in critical areas of the closure.